I have a 2000 MB E320 that sits at home in the summer relatively unused. It has 60k+ on it, is in excellent shape, but the premium fuel costs are a killer. Questions for the forum: Can I use regular in it? If I do, what will happen to the engine? Is this a good candidate for a trade in for a hybrid? thanks,

If you do a lot of highway driving, a hybrid is not for you. Only if you do a lot of stop and go driving will you get the full benefit of a hybrid.

From the looks of it, you don’t drive the MB very much, so fuel costs shouldn’t be as important as if you used it every day. Most often, high octane fuel is 20 cents cheaper than low octane. If you have a 20 gallon tank that you run bone dry before you fill up, the cost will only be $4 more than if you filled up with low octane. When put in that perspective, does high octane really seem that expensive?

Perhaps I was unclear. Can anyone tell me rather precisely what damage would occur to the engine if “regular” is used. Would the injectors foul? Would the timing be disrupted? what? As for the cost of premium in Florida, it is often 50cents per gallon higher and I only use the car around town now. In the summer months, I am in rural MN and use a 2002 Cadillac which gets over 24mpg and often higher. No problem there as it uses regular. Thanks for the responses. All are welcome.

Here in Atlanta, they shifted the grade level price by 5 cents a grade level. Now, premium is 30 cents more per gal. Is it only around here?

And to answer the OP, how can you justify owning a $50,000 car, then bitch about $4 extra per gallon n to fill it? I drive a Supra. It requires 91 octane. I alternate between 89 octane and 93 octane, and fill up on half tanks. Half tanks (7-8 Gals) is about $30-$35. I bitch because of the base price of gas, not the difference between grades.

Again, read the owner’s manual. If Premium is required, stick to it. MB repairs will cost you much more than $10 per full tank. The engine will retard the timing to cope with the lower octane. But, if it cannot retard enough (the ECM does have limits), the pre-ignition damages valves, pistons, connecting rods, and the bearings in-between. It will shorten the lifespan of the engine. Not right away, but the damage accumulates, and will never correct itself. You’ll here a tick that just seems to get louder, and louder, and louder. And, that’s if the engine seems to run OK on it.

If you don’t wanna spend that much, trade it in. You’ll get $10,000 for your trade-in, probably less, and it will cost $30,000 for the hybrid. Plus, get in line. The hybrids all have waiting lists.

Quick math shows that if you drive about 10,000 miles a year in the MB, your paying $2700 in premium gas. The Prius, if you achieve the optimal mileage will cost you $1000 in gas for the same 10,000 miles. But, you’ll have to pay off a new loan of $20,000 for the priviledge.

Thanks for the precise information, and it has answered my questions and determined for me what course I will take. But I wonder at the reasons for the extreme hostility exhibited in answering an honest question. Can only knowledgeable car owners ask questions here without being berated for doing so?

You asked for “…precisely what damage would occur to the engine if “regular” [octane gasoline] is used.” I answered that the gamble is holes burned/detonated into the pistons. Of course, GAMBLE, also, means that nothing untoward may happen. You lessen, or increase, your chances, as you wish. I can only advise from the best knowledge and judgement that I have.

Another answer, previously entered here in cartalk, is that using regular fuel in a vehicle optimized for premium is a bad choice because the MPG will drop more than the pennies saved. This kills the cost savings of moving to regualr and also induces risk of damage; a lose/lose situation.

The type of engine damage you are risking is holes punched in the tops of your pistons due to “detonation”. Personally, I do not believe the difference between 87 and 91 octane is enough to cause destructive detonation. That’s only 4 octane points and most engines can absorb that without any problems. In any case, you will be able to HEAR any spark knock or detonation problems long before any engine damage is done. Engines can tolerate a light “ping” literally forever without suffering any damage. Todays unleaded fuel engines have comparatively low compression ratios, the factor that determines octane need, so even if they DO knock a little now and then, it will not be destructive. Many people who have premium fuel cars put regular in them and they can detect no problems at all…The third owners of these luxury cars are certain to put regular in them. Tearing down an engine and finding holes in the pistons is a rare event indeed…A lot of this “engine damage” is urban legend stuff…Should you detect detonation under full throttle acceleration (that’s the only time it’s likely to occur) you can simply lift your right foot to stop it…

Detonation is most likely to occur under high load, high acceleration, conditions. Some say to lift your foot from the gas pedal when you hear ping. That sounds good; but, how many people even know what ping sounds like? In a panic situation, such as attempting to enter the travel lane (70 mph traffic) from the entry lane, how many people will hear the ping, and (still in a panic to enter mode) lift their foot from the gas pedal? To keep from putting yourself into that extra-awareness position, you can just use the octane which is unlikely to cause ping. Heads, or tails?

As others have said, your best bet is to use the fuel recommended in your owner’s manual. Even if low octane fuel doesn’t cause expensive engine damage, gas mileage will go down. If you want a detailed explanation, I suggest you contact Mercedes Benz Customer Assistance.

The biggest reason you are spending so much on fuel is that its price has tripled in only a few years. The next reason is that, although your car isn’t a gas guzzler, neither is it a gas sipper. According to the EPA, its average fuel consumption is 21 mpg. A Toyota Camry Hybrid is rated at 34 mpg. Your MB burns 60% more than the Camry. The price difference between premium and regular is at most 10%. (Where I live, it’s only 5%).

Think carefully before trading off a premium luxury car like yours just to save some money on fuel. I looked up the following data. Assume premium costs $5.00 per gallon and regular is 10% cheaper. Your MB is worth about $10k as a trade. Its fuel cost is 24 cents per mile. MSRP for a Toyota Camry Hybrid is about $26k. Its fuel cost is 13 cents per mile. Although the Camry costs less to drive than your MB, you would have to drive it 145k miles to break even. Since the two cars you mentioned are an MB and a Cadillac, I doubt you would be interested in a Prius. Even though a Prius is a bit cheaper to buy and much cheaper to drive, you would still have to drive it 100k miles to break even.

I suspect the big reason for the angry replies is an underlying assumption that anyone who can afford $50k for a car, instead of $10k or $20k, doesn’t need to sweat an additional $1k or $2k per year for fuel. I’m in somewhat the same situation as you. Last fall, I spent over $40k on an Infiniti G37S that averages 24 mpg on premium. Since I bought the car to enjoy, not to minimize my cost for transportation, I don’t sweat things like the $130 I just spent getting it detailed or the difference in fuel cost between it and an econobox.

Your MB is a fine car. I recommend you enjoy it and regard the extra it costs in fuel and maintenance as the price of entertainment.